Prior Art
Aerosol type dispensers have been in wide use for many years. The most commonly used type has been a container in which is contained a liqiud material to be dispensed. In a very common arrangement, in the space within the container above the liquid is a pressurized gaseous propellant which exerts a pressure on the liquid. A dip-tube extending downwardly into the container and having a valve means at the top thereof, normally pushbutton actuated, acts as a control to release the fluid, which is forced through the dip-tube from the interior of the container by the pressure of the propellant on the upper surface of the fluid.
With respect to the propellants used in such dispenser, one common system is the system which uses an alcohol solution of the material to be dispensed and the propellant is Freon which is largely dissolved in the solution, and has a gaseous phase normally in equilibrium with the solution on the order of 60 PSIG (about 4KG/cm.sup.2 above ambient). While this produces relatively good atomization of the fluid being dispensed, with droplet sizes on the order of 10 microns or less, it has the major disadvantage that the propellant is relatively expensive as compared with some other gases which might be satisfactory as propellants, and moreover it is incompatible with some products which it might be desired to dispense from such an aerosol type dispenser.
Moreover, Freon has recently come under attack not only as being dangerous from a medical standpoint when inhaled, but also as having an adverse effect on the ionosphere. Consideration is currently being given to banning the use of Freon as a propellant for dispensing material from aerosol type dispensers.
A second common system is the so-called aqueous system in which the product is in an aqueous solution and a hydrocarbon propellant, such as isobutane or isobutane-propane mixtures are used, the gaseous phase of which is in equilibrium with the aqueous phase at pressures of about 45 PSIG and above. However, despite the use of an aqueous solution, there is still some danger from the use of hydrocarbon propellants because they are flammable. Moreover, they are also incompatible with certain materials which it might be desired to dispense with aerosol type dispensers.
Compressed carbon dioxide has been tried as a propellant, but because of its characteristics it has been found that in conventional aerosol dispensers the spray is coarse or barely satisfactory when the CO.sub.2 is at high pressure just after the dispenser has been filled and charged with propellant and for a time until about half the product has been dispensed. Thereafter the atomizing and spray pattern deteriorate to an extent that dispensing is unsatisfactory for many purposes. While CO.sub.2 has been used where such deteriorating of the atomization and spray pattern are of no concern, e.g. in the dispensing of foodstuffs, it has not been found to be useful in areas where atomization and spray patterns are important, e.g. in dispensing of medicaments, hair sprays and other similar consumer products.
However, the properties of CO.sub.2 such as its inertness and solubility over a good temperature range, and its low cost as compared to other propellants, make it an attractive propellant from a commercial standpoint.
It would be highly desirable if an aerosol dispensing package could be provided which made possible the use of carbon dioxide as the propellant for dispensing of solutions of a product without having any significant detrimental effect on the fineness of the spray of fluent materials being dispensed during the course of dispensing the product, so that the drawbacks of using Freon or a hydrocarbon propellant can be avoided.